1. Field of the Invention
The present invention relates to a display fluorescent lamp used as a light emitting device for use in, for example, a large image display unit or an electric sign board, and further relates to a display device.
2. Description of the Related Art
FIGS. 1 and 2 are a perspective view partially broken away of, and a sectional view of a conventional display fluorescent lamp disclosed in, for example, Japanese Patent Publication (Kokai) No. 5-190152. In the drawings, reference numeral 1 means a display fluorescent lamp, 2 is a cylindrical glass valve forming the display fluorescent lamp 1, and 3 is an internal electrode inserted into the glass valve 2 through a lower end surface of the glass valve 2. Further, reference numeral 4 means an external electrode mounted on an outer surface of the glass valve 2, 7 is a fluorescent substance layer formed on inner walls of a side surface and the lower end surface of the glass valve 2, and 8 is a light emitting portion having permeability mounted onto an upper end surface of the glass valve 2. A power source 6 is connected between the internal electrode 3 and the external electrode 4 via lead wires 5a and 5b.
A description will now be given of the operation. When the power source 6 applies ac voltage across the internal electrode 3 and the external electrode 4, the voltage is applied to a rare gas in the glass valve 2 through glass serving as dielectric material, thereby causing discharge. Ultraviolet rays are generated by the discharge to excite the fluorescent substance layer 7, and are thereafter converted into specific visible rays which are determined depending upon fluorescent substances.
Since a fluorescent substance itself has a white body, the visible rays emitted from the fluorescent substance are substantially totally reflected off the fluorescent substance layer 7 mounted on the inner wall of the glass valve 2, and are thereafter sent back into the glass valve 2. The visible rays can be outputted and emitted out of the glass valve 2 through the light emitting portion 8 exclusively having permeability. Thus, the display fluorescent lamp 1 serves as a light emitting device having high luminance.
The conventional display fluorescent lamp can serve as the light emitting device in a large image display unit to provide suitable emission with high luminance. However, with higher resolution of the large image display unit, it is necessary to reduce a diameter of the glass valve 2 for higher density arrangement of the display fluorescent lamps 1. Hence, a distance between the internal electrode 3 and the external electrode 4 is more reduced, resulting in problems in that, for example, a sufficient creepage distance can not be ensured for electrical insulation.